In modern road toll systems, vehicles subject to tolls are equipped with on-board units (OBUs), which can be used to locate the vehicles so as to then charge tolls (fees) for their usage of the road. The OBUs can take on a variety of designs: The OBUs can be of the “self-locating” type, which is to say, they can continually determine the locations thereof themselves, for example by means of a satellite navigation receiver as part of a satellite navigation system (global navigation satellite system, GNSS) and report the locations thus determined (“position fixes”) either directly to a back office of the road toll system, be it via a mobile communication network or a network of geographically distributed radio beacons, or in the form of “abstracted” toll transactions, which are calculated based on the reported positions. As an alternative, such GNSS OBUs could simply store the reported positions or toll transactions thereof, or debit the fees calculated based thereon from an internal toll credit account. The OBUs can also be of the “externally located” type, for example using a plurality of toll or radio beacons which are geographically distributed over the road toll system and which establish the respective short range communication or DSRC (dedicated short range communication) with passing OBUs and localize them with respect to the known beacon locations thereof due to the limited communication range. Corresponding reported positions, or toll transactions calculated based thereon, can then be generated by the OBUs or the toll beacons and processed either in the OBUs or in the back office.